Rapid prototyping or solid free-form fabrication has become an increasingly important tool, and is a technology that has seen great advances since its initial application in the 1980s, evidenced in U.S. Pat. No. 4,575,330, which is incorporated by reference herein as if fully set forth below. In one common embodiment known as stereolithography, rapid prototyping manufacturing makes use of a bath of curable liquid, wherein some movable point within the bath is subjected to stimulation by a prescribed curing source. As the source is moved with respect to the bath or as the bath is moved with respect to the source, the point that undergoes solidification or curing is constantly made to move. The result is the construction of a solidified mass of cured material contained within the otherwise liquid bath. The region commonly solidified is positioned at or very near the surface of the bath in most practical applications. As the liquid is solidified, the solid structure is progressively lowered into the bath allowing the uncured liquid to flow over the surface, which is in turn subjected to the same process. By continuing to solidify these very thin layers, the solid object is built up into its final shape. Bonding of one layer to a previous layer is an inherent property of the process as is known in the art.
For example, photolithography systems that direct light beams onto a photosensitive surface covered by a mask, etching a desired pattern on the substrate corresponding to the void areas of the mask, are known in the art. In mask-based photolithography systems, the patterns generated are defined by physical masks placed in the path of light used for photo-activation. While effective, the use of physical masks in photolithography has numerous drawbacks, including the cost of fabricating masks, the time required to produce the sets of masks needed to fabricate semiconductors, the diffraction effects resulting from light from a light source being diffracted from opaque portions of the mask, registration errors during mask alignment for multilevel patterns, color centers formed in the mask substrate, defects in the mask, the necessity for periodic cleaning, and the deterioration of the mask as a consequence of continuous cleaning.
Maskless photolithography systems are also known in the art and often use an off-axis light source coupled with a digital micromirror array to fabricate chips containing probes for genes or other solid phase combinatorial chemistry to be performed in high-density microarrays.
While maskless photolithography systems address several of the problems associated with mask-based photolithography systems, such as distortion and uniformity of images, problems still arise. Notably, in environments requiring rapid prototyping and limited production quantities, the advantages of maskless systems as a result of efficiencies derived from quantities of scale are not realized. Further, while maskless photolithography systems are directed to semiconductor manufacturing, these prior art systems and methods notably lack reference to other applications lending themselves to maskless photolithography techniques.
A commonly-used curable medium includes photopolymers, which are polymerizable when exposed to light. Photopolymers may be applied to a substrate or objects in a liquid or semi-liquid form and then exposed to light, such as ultraviolet light, to polymerize the polymer and create solid coatings or castings. In addition, conductive photopolymers are known that exhibit electrically conductive properties, allowing creation of electric circuits by polymerizing the polymers in circuit layout patterns. Conventional methods of photopolymerization, however, use physical masks to define areas of polymerization. This mask-based photopolymer process suffers from the disadvantages of mask-based photolithography methods, including the requisite need for many different masks, long lead time for mask creation, inability to modify masks, and the degradation of masks used in the manufacturing process.
As one may imagine, there are many advantages of rapid prototyping. For example, the rapid prototyping process has the ability to drastically reduce the time between product conception and final design, and to create complex shapes. More traditional modeling or prototyping is obtained from an iterative generation of a series of drawings which are analyzed by the design team, manufacturing, the consumer, and perhaps others, until a tentative final design results which is considered viable. This agreed upon design is then created by casting and/or machining processes. If molds are needed, these must be fabricated as well, which may take considerable and valuable time. The finished prototype is then tested to determine whether it meets the criteria for which the part was designed. The design and review process is often tedious and tooling for the creation of the prototype is laborious and expensive. If the part is complex, then a number of interim components must first be assembled. The prototype itself is then constructed from the individual components.
Use of rapid prototyping significantly reduces the expense and time needed between conception and completion of the prototype. Commonly, the concept is rendered in CAD (computer aided design). As this process is fully electronic, drawings are not required for fabrication. The CAD system is used to generate a compatible output data file that contains information on the part's geometry. This file is typically converted into a “sliced” data file that contains information on the part's cross-section at predetermined layer depths. The rapid prototype control system then regenerates each cross-section sequentially at the surface of the curable resin. The fabricated part may be analyzed by the team or used for various form, fit, and functional tests. Due to the rapid speed and low cost of the process, several designs may be fabricated and evaluated in a fraction of the time and for significantly less than it would take to machine each concept. Because the rapid prototyping process creates the structure by the creation of very thin layers, complex components with internal complexities may be easily rendered without requiring the assembly of a plurality of individual components.
On the other hand, one conventional and significant disadvantage of rapid prototyping, other than initial costs to implement technology, is that the time associated with the creation of each part may still be longer than desired. Because creation of the part occurs in a point-by-point, layer-by-layer process, the time necessary to produce a single part may become excessive. Reduction in fabrication times continues to be a desirable goal. Though the above description pertains to the process of stereolithography; the process, as well as the general advantages and disadvantages are similar for other rapid prototyping technologies.